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Meaghan Ormsby, MS, RDN

Life in the northwest can feel pretty dreary in the winter time — the sky is dark and the days are short. By now, many of us have heard about how life in this wet, dark corner of the U.S. is likely making us vitamin D deficient, but what does this really mean? How does it affect us? If you have no idea whether or not you’re at risk of “D-ficiency” or if you are unsure of how relevant it is to you, read this and we’ll help you sort it out.

What is vitamin D?

Vitamin D is called the “sunshine vitamin” because it’s made in your skin when exposed to sunlight. It is a fat-soluble vitamin, meaning that dietary fat is required for absorption and that it can be stored in our body fat.

What does vitamin D do?

Vitamin D’s main role is helping with calcium and phosphorus absorption. Without enough vitamin D we can suffer the consequences of calcium deficiency – poor teeth health and poor bone growth and maintenence, and possibly osteoporosis (brittle bones, at higher risk for fracture) or in children, rickets (deformed bones or fractures).

Vitamin D also has a role in in serotonin (the “feel good neurotransmitter”) synthesis as well as in helping to mediate our stress response. Understanding of these mechanisms has led to research on D and Seasonal Affective Disorder (SAD). Symptoms of SAD include:

Decreased energy

Feeling sad most of the day on most days

Sleep disruption

Difficulty concentrating

Losing interest in previously enjoyed activities

Appetite changes

The jury is still out on the effect of vitamin D deficiency on SAD – there is research on both sides of this, some showing little connection between low vitamin D and mood, and other research shows promise for vitamin D supplementation as a treatment for SAD in individuals who are deficient in vitamin D. But most medical practitioners in the Northwest recommend that SAD patients with low D begin supplementing to correct the deficiency and optimize mood. Additional treatments may also include medication, psychotherapy, and light therapy.

Other functions: some studies show vitamin D playing a role in cancer risk, specifically in preventing prostate, breast, and colon cancer. Other research suggests that D also plays a role in decreasing risk of developing multiple sclerosis, heart disease, and the flu. Some treatments of diabetes, high blood pressure, and arthritis have included vitamin D supplementation, but check with your doctor before adding vitamin D to treat disease.

What are sources of vitamin D?

Our bodies naturally synthesize vitamin D, however it requires bright, direct sunlight for this to occur. Although it only takes 15-20 minutes of skin exposure to get nearly a week’s worth of your D requirement, this is hard to come by in Seattle winter when we’re not only short on bright sunlight, but our bodies are bundled up as we try to stay warm. Season, time of day, length of day, cloud cover, smog, skin melanin content, and sunscreen are among the factors that affect sun exposure and vitamin D synthesis.

We also get vitamin D in food, however it can be very difficult to get all we need from food, especially in the Northwest. Milk, egg yolks, fortified milk, and fatty fish contain the highest amount of vitamin D. The Institute of Medicine (IOM) recommends we consume at least 600 IU (International Units) per day, and 800 IU per day if you are over 70 years old. 3 ounces of salmon or swordfish contains 450-550 IU vitamin D, milk contains ~120 IU, and eggs 41 IU. Dietary patterns increasing risk of deficiency include milk avoidance – whether it’s an allergy or lactose intolerance, vegetarianism, and veganism.

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